In order to determine whether estrogen replacement therapy can reverse many of the identified CAD risk factors, we will measure lipoproteins, hepatic lipase activity, and body composition in 90 premenopausal women who have large, buoyant LDL particles, and repeat these measures when they are postmenopausal and at one and 12 months of estorgen replacement therapy. The study will determine the effect of estrogen deficiency on these characteristics and the inter-relationship amongst them. It is proposed that those women who develop LDL subclass phenotype B will return to phenotype A with estrogen replacement therapy.